The present invention relates to a procedure for controlling ling an elevator group.
The function of elevator group control is to allocate the landing calls to the elevators in the group. The allocation of landing calls in group control may depend on factors such as load situation of the elevator group, number and disposition of calls, and instantaneous load, position and travelling direction of the elevators. In modern group control, attention is also paid to controlling passenger behavior. Call allocation in group control is the result of an optimisation task in which various parameters related to travelling comfort and other aspects of elevator use are optimized. Such parameters include e.g. waiting time, advance signalling capability, energy consumption, transport capacity, travelling time and equalization of car load. In modern microprocessor based control systems it is possible to optimize several parameters simultaneously.
Advance signalling is an important part of passenger guidance. Advance signalling is used to guide the passengers at a timely stage to the vicinity of the doors of an elevator arriving at a floor. Advance signalling does not require the use of extraordinary call button arrangements at the landing. Timely advance signalling or immediate assignment of the elevator to be allocated to the call can be best accomplished by using a control system with future-oriented simulation in which possible future situations have already been taken into account when signalling is being given or an elevator is being assigned to a call. EP patent specification 568 937 presents a procedure for controlling an elevator group in which future situations are taken into account. This procedure uses a decision analysis which is executed each time when an elevator arrives at a point where the system has to decide which one of alternative solutions is to be selected (e.g. passing by or stopping at a floor). The decision analysis examines the effects resulting from different alternative control actions by simulating the behavior of the system in the situation after the decision. In this procedure, a decision is made at two different terminations: At the starting point, where the elevator is standing at a landing with doors closed and ready to depart, and at the stopping point, where the elevator is moving and arrives at the deceleration point of the destination floor.
GB patent specification 2 235 311 presents a group control method for an elevator system in which a suitable control algorithm is selected by simulating different control modes and selecting control parameters corresponding to specified target values. In this method, statistics are maintained about the distribution of car calls issued for a given floor. This information is utilised in predicting stoppages due to car calls. However, the prediction ends with the call being served and does not actually take into account any events subsequent to the point of time when the calls are served.
The object of the present invention is to improve the existing group control procedures. Among other things, it is an object of the invention to achieve a better ability to anticipate future situations so as to facilitate advance signalling and allocation of calls to the elevators. It is also an object of the invention to ensure better consideration of both the states of the elevators and the situation regarding landing calls when allocating elevators to landing calls. In the procedure of the invention, the instant of decision is associated with the activation of a new landing call. In other words, primarily no decisions are made when there are no active landing calls. At the instant of decision, probable future landing calls are simulated, and these are allocated to the elevators in accordance with an optimum policy by calculating simulated costs and a new call is allocated to the one of the elevators whose use will result in the lowest cost on an average. In simulating the future, passengers are generated for different floors in proportion to arrival intensity and distribution; similarly, car commands are generated in accordance with probable intensities of passengers leaving the elevators. A call is not finally reserved until in a certain time window. In practice, thanks to improved forecasts of future situations, the invention makes it possible to achieve an improved accuracy and stability of call allocation in group control.
According to the invention, simulation and call reallocation can be performed even for old calls that are only going to be served after a certain length of time, which means that the simulation of future operation regarding these calls can be performed using even calls that in reality have been registered only after this call.